1. Field of the Invention
The invention relates to a catheter comprising a valve for controlling fluid (especially liquid) at its distal end by which it is inserted into a duct of a human or animal body, in order to control the distribution of fluid from the catheter into said duct or the removal of fluid from the duct.
In particular, the catheter of the invention is a vascular catheter adapted to be inserted into a vessel in such a manner that its distal end is located therein, either in order to remove blood, for example, from the vessel or to inject a treatment product into the vessel.
2. Description of Background Art
Several intravenous therapies, including the administration of chemotherapeutic medicaments and hyper-feeding, require the use of such a vascular catheter that is suitable for remaining in the patient's body for an implantation period that may sometimes last several weeks.
Typically, such a catheter is implanted by the femoral or jugular route (then through the subclavian vein, towards the upper vena cava).
Of the existing vascular catheters, that of EP-A-328 332 (or U.S. Pat. No. 5,030,210) is known in particular.
As in the invention, it is a "two-way" catheter for controlling the circulation of fluid through it from, or to, a duct of a human or animal body in which the catheter is inserted.
That catheter has a principal axis and comprises:
a long tubular body extending along the principal axis and having an internal passage, an inside diameter, an outside diameter, and a distal end having an opening that communicates with the passage, PA1 a cap that is located over the open distal end of the body and is fixed to the body, the cap having an essentially flat distal wall facing the open distal end of the body, PA1 and at least one slit forming a valve that is formed through said flat distal wall of the cap, to communicate with the passage in the body of the catheter, the valve reacting to pressure differences on either side of it, for the circulation of fluid from, or to, the duct. PA1 that the cap has a substantially cylindrical side wall, PA1 that the cap has an inside diameter that is comparable to, and preferably larger than, the inside diameter of the body of the catheter, PA1 and that the slit(s) forming the valve extend(s) both over the distal wall of the cap and into its cylindrical side wall. PA1 the valve comprises at least two slits arranged in a cross, each slit having a length of approximately from 3 mm to 4.5 mm, PA1 and the cap has an outside diameter of approximately from 2.2 mm to 2.8 mm and an inside diameter that is more than approximately 0.3 mm larger than the inside diameter of the body of the catheter. In both cases, the distal wall of the cap, in which the valve is formed, will of course extend at a distance from the distal end of the body of the catheter.
In the above-mentioned patent it is indicated that the catheter disclosed therein has been optimised for the circulation of liquid, within the context of intravascular implantation.
In particular, it is indicated therein that the problem of circulating liquid in both directions (from or to the catheter) has been taken into consideration; the proposed catheter is supposed to provide such bi-directional operation, in particular without causing the catheter to fold or collapse in on itself on aspiration.
The proposed solution also claims to provide the distal end of the catheter with a structure that is sufficiently thick that it will not fold or become blocked as a result of movements of the patient, muscular movements or an aspiration vacuum; moreover, the valve slit arranged in a relatively thin wall covering the open distal end of the catheter is said to permit a rapid reaction of the valve to differences in pressure.
The catheter of EP-A-328 332, or U.S. Pat. No. 5,030,210, has a catheter body preferably made of polyurethane and having a thickness of approximately from 0.25 to 0.75 mm. The cap has a wall thickness of preferably from 0.05 to 0.25 mm. Silicone rubber, polyvinyl chloride, polyethylene or polytetrafluoroethylene may also be used. A single slit forming a valve is provided, its length being approximately from 30 to 70% of the inside diameter of the catheter. The slit arranged in the distal end wall of the cap is flattened against the open distal end of the body of the catheter, in such a manner that there is no gap between the distal ends of the body and of the cap.
Within the context of the present invention it is maintained that a further real improvement in operation, especially on aspiration, can be achieved and that a further improvement can likewise be obtained in the manner in which the problem of the wall surrounding the valve slit collapsing in on itself is resolved, in particular within the context of vascular catheters provided for injecting a treatment liquid into a vessel in one direction and, in the opposite direction, for allowing the removal of, especially, blood or a body fluid.
For bi-directional operation to be possible it is essential to ensure that the valve will open correctly (in one direction or the other) for a predetermined pressure difference and that it will remain closed, by its lips being in contact with each other, if that pressure difference is not achieved, without damaging the integrity of the catheter, its necessary flexibility associated with mechanical strength, and the resistance that must be provided in view of the consequences of unexpected movements of the catheter inside the patient's body.
In accordance with the solution of the invention, the catheter described above in connection with EP-A-328 332 has a cap, the slit(s) of which has (have) a length that is at least equal to the inside diameter of the body of the catheter. Another characteristic that is also used to solve in particular the problem of the walls surrounding the slit forming the valve collapsing in on themselves, especially on aspiration, is that the flat distal wall of the cap is located at a distance from the distal end of the body of the catheter.
Especially with such a characteristic, and if the distal wall of the cap is in the form of a full circular disc that is split, it will be possible to lengthen the slit(s) in such a manner that the length of the slit(s) is greater than the outside diameter of that wall. In fact, it has been found that very good operation is obtained if the length of the slits(s) (especially two slits in a cross extending in two perpendicular directions) is (per slit) from 1.5 to 2.5 times the inside diameter of the catheter, that is to say in fact much greater than the outside diameter of the cap, since that outside diameter is only several tenths of a millimeter (indeed possibly several millimeters) larger than the inside diameter of the body of the catheter.
A further problem to be solved by the invention concerns the flow rate of fluid that is to be able to pass through the valve. In fact, it has been found that existing "two-way" catheters only allow flow rates that are too weak to satisfy the users' requirements. Therefore, the invention solved that problem, by requiring, moreover, that the flow rate through the valve be comparable to that which would exist for the same catheter, but without a cap, and for the same pressure. It is likewise to be noted that while designing the present catheter it was found that the problem to be solved is associated both with the manner in which the valve is formed and with certain characteristics of the cap.